The present invention relates to industrial inspection of manufactured items and more particularly to the detection of, for example, the presence or absence of parts, the identification of parts, and their position or orientation, all automatically.
Prior art inspection apparatus has, for the most part, involved the use of a black and white television camera which observes the manufactured item and operates to produce a video output signal representative of the item. The signal is presented to an image processor which assigns a binary or gray scale digital value to each pixel of the picture in accordance with the amount of black and white at that point in the overall image. The digital representation of the image may then be compared with a standard image or picture (template matching) or, in more advanced systems, the individual pixels will be used by a computer in the image processor to compute the area, perimeter, coordinates, orientation, etc. of the parts. The parts are known by the contrast they have with the background and thus digital information is obtained as to the various features of the item which are needed to identify it or its parts. The information which is gathered concerning the area, perimeter, orientation, etc. may then be stored in a memory of the computer in the image processor and then compared or matched with predetermined or known values programmed into the computer so as to attempt a match area, perimeter, orientation, etc. If a match occurs within the proper tolerance, an identification is made of the part, its location, etc. The output of the image processor may be a display for use by a human operator or may be command to a machine or a robot device for selecting, placing or passing the part.
A difficulty arises when parts differ from their background only in color and cannot be recognized in black and white, or when parts of the same shape and area differ only in color since they may appear the same when analyzed in black and white. As an example, the color coding on a resistor identifies its value and yet the resistor is of the same size and shape as the resistor of a different value for all practical purposes and gray scale analysis of color coded bands is not a reliable code indicator. Likewise a capacitor may have exactly the same size and shape as a resistor but is of a different color and the identification of that capacitor depends upon the identification of the color involved. Also the capacitor may be of very similar gray level as the underlying circuit board and cannot be distinguished even though the board is green and the capacitor is red.
Prior art systems have tried to handle this problem by utilizing a color television camera and then processing the Red, Green, and Blue (RGB) signals with three separate image processing devices to assign digital values for each of the color components and then marrying the results and comparing them to determine the color as well as the other features of the part being observed. Unfortunately, such systems are quite costly in that they involve three separate image processing paths and they take considerably more time than is desired.